Process for production of normal paraffins from middle distillate by urea adduction



' NAokl YATA ETAL 3,506,569

April 14, 1970 v PROCESS FOR PRODUCTION OF NQRMAL PARAFFINS FROM MIDDLEDISTILLATE BY UREA ADDUCTION Filed Dec. 26. 1967 3, MZWDJOP mm mzuaJoh.uzuaoh wn MZMDJOP United States Patent Int. (:1. coin 21/00 US. Cl.208-308 10 Claims ABSTRACT OF THE DISCLOSURE A process for theseparation of n-paratfins from bydrocarbon distillate by means ofpowdered urea is provided, wherein hydrocarbon distillate is treated inthe presence of an activator solvent of methanol and aromatichydrocarbon together with powdered urea, and then resulting urea adductis separated from the liquid part of the reaction mixture. The adduct isthen washed with aromatic hydrocarbon, and decomposed by heating in adecomposition medium consisting of 5 to 30 percent by volume ofn-paraflins and 70 to 95 percent by volume of aromatic hydrocarbons. Thethus obtained urea is then separated from the n-paraffin product, and isrecycled into the process.

BACKGROUND OF THE INVENTION The present invention relates to the methodof separating n-paraffins of high purity from hydrocarbon oils, inparticular from middle distillate fractions of petroleum, whichhave aboiling point over the range of about 100 C. to 440 C.

Numerous methods of lowering the pour point of Inbricating oil stocks bytreatment with solid urea have been proposed in the prior art. Forexample US. Patent 2,911,350 (1959) discloses such a process. Howeverthe main object of these methods is to lower the pour point oflubricating oil stocks, and problems concerning both the purity of.then-parafiins obtained after the decomposition of adduct, and the methodof n-parafim recovery have almost been neglected.

There are, many methods of urea adduction using an aqueous solution ofurea for extracting n-parafiins from middle distillate, but thedisadvantage of these processes is that the purity of the thus-extractedn-paraflins is low, because oil components other than n-parafiinssolubilize in the water phase which is coexistent with the n-paraffinadduct, and extreme contamination-by these components is found in theproduct obtained after decomposition of the adduct.

BRIEF SUMMARY OF THE INVENTION The principal object of this invention isto provide a method of extracting n-paraiiins in substantially highpurity and in good yield by means of urea adduction technique usingsolid or powdered urea.

Another object of the invention is the provision of a method forextracting n-paraffins using urea wherein the disadvantages present inthe prior art processes have been eliminated.

Another object of the present invention is to provide 3,506,569 PatentedApr. 14, 1970 effective activators for urea adduction, thereby improvingthe effectiveness of adduct decomposition.

Still another object of the present invention is to provide a continuousadduction process which is more economical than hitherto proposedprocesses.

A particular object of this invention is the provision of a method forobtaining high purity n-paraffins in high yield from middle distillates,such as kerosene or gas oil fractions of petroleum oil.

It has been discovered that these and other objects can be attained byan improved process for production of n-paraffins from a liquidpetroleum fraction by urea adduction, which comprises treatinghydrocarbon oil with solid urea in presence of an activator solventwhich consists of a mixture containing methanol and aromatichydrocarbon, wherein methanol is present in an amount of 3 to 30 percentby volume.

According to the invention, the n-paratfin product is obtained by thefurther steps of separating the resulting adduct from the liquid portionof the reaction mixture, washing the thus-obtained adduct with aromatichydrocarbon, decomposing the adduct by treatment with 1.5 to 5.0 volumesof a decomposition medium per volume of said adduct, the decompositionmedium consisting of 5 to 30 percent by volume of n-paraflins,preferably nparaffin which have been previously extracted and thebalance being aromatic hydrocarbon, at a temperature of above C. butbelow the dissociation temperature of said adduct.

BRIEF DESCRIPTION OF THE DRAWING The figure represents a schematic flowdiagram of a plant for the separation of n-paraflins from hydrocarbondistillate and illustrates a continuous process according to the presentinvention.

DESCRIPTION OF THE PREFERRED EMBODIMENT In accordance with the presentinvention, liquid hydrocarbon containing n-parafiins is treated withsolid urea in presence of the activator solvent which consists of amixture of methanol and aromatic hydrocarbon, the methanol being presentin an amount by volume of 3 to 30 percent and aromatic hydrocarbonsmaking up the remaining volume. During the step of forming the ureaadduct, desirably the mixture of hydrocarbon charge oil, urea andactivator solvent are vigorously agitated. The aromatic hydrocarbon usedfor the activator solvent may be a single compound or a mixture of twoor more compounds and is preferably selected from aromatic hydrocarbonshaving 6 to 8 carbon atoms, such as benzene, toluene, xylene andethylbenzene. The amount of the activator used is preferably 5 to 40percent by volume based on the volume of hydrocarbon oil, and as thisactivator solvent is completely soluble in the oil phase, the timerequired to reach the adduct equilibrium is in the range of five toeight minutes. Thus, the time required for adduction time is in strongcontrast to that required for a conventional process using methanolalone.

In the case of conventional processes, methanol tends to form a separatephase upon the oil, and the time required to reach the adductionequilibrium is thirty minutes or more because of the difficulty ofdiffusion of methanol in hydrocarbon oil. Generally speaking, nor- :bymethods using a solution of urea, such as an aqueous solution thereof,but isoparafiins such as Z-methyl-paraffins are adductablc and somequantity of these isoparaffins remains in the extracted portion ascontaminant. It is in such cases that the improvement in the purity ofthe product n-paraffins which results from the method of the presentinvention is most advantageous.

The present invention provides that one volume of ad duct thus obtainedis then retreated with 1.5 to volumes of a contact oil which iscomprised of n-parafiins; preferably the n-paraffins used for this stepof the process are those obtained from previous extraction of chargehydrocarbon oil; or, the adduct may be retreated with the same amount ofa contact oil which is comprised of hydrocarbon charge oil. It has beenfound that an improvement in purity of at least 0.5 percent by weight isobtained, and in some cases an improvement of more than 1 percent byweight is obtained without detriment to the recovery of n-paraffins bythe present method.

The present process is useful for separating n-paraffins fromhydrocarbon distillates ranging from kerosene to gas oils. Thushydrocarbon fractions which having a boiling point of about 100 C. toabout 440 C. may be subjected to treatment in accordance with thisinvention. Hydrocarbon distillate may be used by itself as the chargeoil or it may be mixed with deparaffined oil before being treated.

The following example illustrates the method of the present inventionand also shows the effect on the product of different treatments of theurea adduct.

EXAMPLE 1 Part A.1 kg. of a kerosene fraction from Middle East Crudewhich has a n-parafiin content of 11 percent by weight and a boilingrange of 135 to 268 C. was mixed with toluene-methanol solventcontaining percent by volume of methanol, and 408 g. of powdered ureawas added thereto, and the mixture was stirred for ten minutes at C.After the filtration of adduct slurry by suction, adduct was washed with2,300 ml. of toluene and was decomposed with 1850 ml. of decompositionmedium consisting of 80% by volume of toluene and 20% by volume ofn-parafiin at 80 C. After stirring for ten minutes, the regnerated ureawas separated from the n-parafiins at the second filtration step, 405 g.of product n-paraffins were obtained, after the evaporation of toluene,which represents a yield of 10.8 percent by weight based on the weightof said kerosene after subtraction of the weight of n-paraffin added indecomposition medium. The n-parafiins thus obtained had a purity of 97percent by weight in accordance with gas liquid chromatography as shownin Table 1.

Part B.The same adduct was washed with 5,350 ml. of toluene and 377 g.of n--paraff1ns, and the product nparafiins were then obtained using thesame treatment as mentioned above with the result that 8 percent byweight of n-parafiin were recovered having a purity of 97.3 percent byweight.

Part C.The same adduct was contacted with 2,330 ml. of a mixtureconsisting of 40 percent by weight of nparaffins and 60 percent byweight of kerosene, stirred for ten miutes, filtered, and then thethus-retreated adduct was washed with 3,050 ml. of toluene, after theabove mentioned treatment, 407 g. of n-parafiin were obtained, with arecovery rate of 11.0 percent by weight, and purity of 98.2 percent byweight.

Accordingly, a substantial improvement in recovery and purity ofn-paraffins is obtained by the retreatment step of the inventionillustrated in part C of this example whereas the use of an increasedamount of washing solvent for washing the adduct as illustrated in partB of this example results in a larger decrease in the recovery rate ofthe n-parafiins. These results are summarized in Table 1.

TABLE 1 Adduct Adduet Retreated washed with washed with adduct washed2,300 ml. 5,3501111. with 3,050 ml. of toluene of toluene of tolueneRecovery of n-paraflins (wt. percent of kerosene) 10. 8 8. 0 11.0

Carbon number distribution Wt. percent 0. 7 0. 3 0. 1 3. S 2. 3 1. ii23. l 20. 9 l5. 2 30. 3 40. 4 86. 1 25. 0 27. 2 34. 8 4. 7 5. 5 0. 2 0.7 0. 6 1. 1 trace 0. 1 0. 1

n-parafhn 97. 0 97. 3 18.2

Null Null Null 0.2 0.2 0. 1 0.8 0. 5 0. 4 1. 3 1. 3 0. 8 0.6 0.6 0. 4 0.1 0. 1 0. 1

i-Paraffin 2. 0 2. 7 1. 8

While it might be expected that the concentration of n-paraffins in theoil should be as high as possible for the most effective process,particularly with respect to the contact retreatment or rewashing, ithas been found that there is no marked difference in the effect of theconcentration between 5 and percent by Weight of n-parafiins in the oil,and 10 to 40 percent by weight seems to be preferable. An adequatequantity of the contact oil was found to be 1.5 to 5 volumes per volumeof adduct. Substantially pure substances such as n-parafiins or themixture of n-paraflins and pure aromatic or naphthenic hydrocarbons maybe used instead of the contact oil mentioned above. Paraffinichydrocarbons which have different numbers of carbon from those in thecharge oil may also be used as contact oil. Normal paraffins from chargehydrocarbon oil, or those which have the different carbon number fromthe former are also used as a contact oil. The required contact time inthis case is from about 5 to about 30 minutes or more, preferably from10 to 30 minutes, and temperature range of from 10 to 40 C. ispreferred.

Deparaffined oil which has been obtained by the preceding adduction stepis used as a diluent oil for adduction, to aid the transportation ofadduct slurry.

Adduct decomposition in this invention is carried out at the temperaturebelow the dissociation temperature of adduct, which has been determinedby the method of Knight et al. (H. B. Knight et al., Anal. Chem. 24 1331(1951)). It has been found that in all cases, a decomposition of 60 C.to C. is effective, using a decomposition medium consisting of a mixtureof the extracted nparaifins and aromatic solvent, such as benzene,toluene, xylene and/or ethylbenzene. The concentration of nparafiin inthe decomposition medium may be from 5 to 30 percent by volume,preferably 10 to 20 percent by volume, and the decomposition temperatureis preferably from 70 C. to 90 C. The contact time required for thecomplete decomposition of adduct to solid urea and nparaffins is from 8to 10 minutes under the above mentioned conditions, and it is necessaryto add 1.5 to 5 volumes of decomposition medium to one volume of adductfrom considerations of the transportation of the urea slurry and thedecomposition rate of adduct.

The following example illustrates the decomposition of the urea adductto obtain the nparafiin product in accordance with the presentinvention.

EXAMPLE 2 n-Cctane (n-hexadecane) urea adduct, which has a dissociationtemperature of 1ll.7 C. and a weight ratio of urea to n-cetane in theadduct of 3.8 was decomposed with 4 volumes of a medium containing 10,30, and 50 percent by volume of n-cetane, respectively, while beingstirred for 20 minutes at 80 C. A part of slurry which had undergonedecomposition was filtered and the regenerated urea portion washed witha large quantity of toluene and examined by x-ray diffraction.

Several powder patterns are summarized in Table 2, where (S), (VS), (W)and (VW) means a diffraction intensity which is strong, very strong,weak, and very weak, respectively. It is evidentt from these powderpatterns that complete decomposition was obtained when the concentrationof n-cetane was and 30 percent by volume and the diffraction patternsare quite similar to those of pure urea itself, but in case wherein themedium contained 50 percent by volume of n-cetane, an undecomposedportion of adduct remained.

TABLE 2 Diffraction Didi-action angle of the samples angle ofDiffraction (Volume percent of n-cetane in n-cetane angle ofdecomposition medium) urea adduct pure urea 34. 5 S 37. 4 (S) 37. 4 (S)37. 4 (S) 37. 4 (S) 35. 8 (S) 35. 8 (S) 85. 8 (S) 35. 8 (S) 27.6 (VS)31.9 (S) 31. 9 (S) 31.9 (S) 27. 6 (VS) 29. 5 (VS) 29. 5 (VS) 29. 5 (VS)29. 5(VS) S. 22399 asst; .3 VS 24. 8 S 24. 8 25 t (vs) 22% .3 22. 6 VS22. 6 VS 22.6 2 23 (VW) 2g 22.0 VS 22.0

22.0 (W) 20. 7 (W) 20. 6 (W) 20. 6 (W) 20.6 (W) 20. 6 (W) The especiallypreferred method of the present invention is a continuous process forseparating n-paraffins from a petroleum fraction which will be describedin the following example with reference to the accompanying drawing.

EXAMPLE 3 Gas oil 2, containing 18 percent by weight of nparafiins andhaving boiling range of 190 to 270 C. is charged in an amount of 11,800kg./hr. through line 3 where it is diluted with 17,700 kg./hr. ofdeparafiined oil 4 which has been obtained by previous adduction of thecharge oil; 2,500 kg./hr. of a toluene-methanol mixture 6 as theactivator solvent, containing 10 percent by volume of methanol is alsofed together with said oil mixture through line 3 to the reactor 7 whichis provided with agitation means adequate to provide vigorousliquidsolid mixing; 8,700 kg./hr. of recycled urea 8 is also chargedinto reactor '7 through line 3-. The slurry of urean-paraffin adduct isdischarged from reaction vessel 7 through line 9 and sent to asolid-liquid separator 11 which is equipped with means for separatingthe urea adduct from the unreacted liquid such as a suction filter or acentrifuge. After the adduct is separated, it may be washed in thesolid-liquid separator 11 with a liquid aromatic hydrocarbon 10, toluenebeing used in this process, and after being washed, the adduct may besent through lines 13 and 15 directly to the decomposition vessel 17, itthe purity of n-paraffins produced in this way is satisfactory. If ahigher purity product is desired, the adduct separated in thesolid-liquid separator 11 is sent by way of line 13 to the retreatmentvessel 19 which is provided with means for agitation. The liquidfiltrate from the solid-liquid separator 11 is discharged through line21 and sent to storage vessel 23-. From storage vessel 23 the filtrateis sent to the solvent recovery tower 25'; the distillate from the topof tower 25 is sent through line 27 to distillation tower 29', a mixtureof toluene and methanol being collected from the top of tower 29 andtoluene from the bottom. The bottoms from the, solvent recovery tower 23is sent through line 31 to distillation tower 33; toluene is recoveredfrom the top of tower 33 and deparaflined oil from the bottom.

Contact oil 34, in an amount of 24,000 kg./hr. is also charged from line35 to line 13 and into the retreatment vessel 19 where it is agitatedwith the adduct.

The contact oil is charge oil, or a mixture of charge oil andn-paraffins which have been separated previously from the charge oil.The slurry of adduct and charge oil is discharged from vessel 19 throughline 37 and sent to the solid-liquid separator 39, where the adduct isseparated from the contact oil by means such as filtration orcentrifugation and is then washed with about 30,000 kg./hr. of toluene40. The solid-liquid separator 39 is equipped with means such as atrunnion valve for discharging separately, the filtrate from theseparation of adduct and contact oil, the filtrate from washing theadduct, and the washed adduct. Thus, the washed adduct exits from thesolid-liquid separator 39 through line 41 and 'is then sent to thedecomposition vessel 17 which is equipped with heating means andagitation means. The filtrate from the separation of the adduct and thecontact oil in the solid-liquid separator 39 is withdrawn through line43 and sent to the storage vessel 45, and the toluene wash from thesolid-liquid separator 39 exits through line 47 and is sent through line21 to storage vessel 23. Through line 41, 24,000 kg./hr. of a recycledmixture of 4 volumes of toluene and 1 volume of n-paraflins is alsocharged into the decomposition vessel 17. The mixture of toluene andn-parafiins are sent to line 41 from storage vessel 49, through line 51.The adduct is then decomposed under contiuous agitation and heating inthe decomposition vessel 17 at a temperature of 75-80 C. Then, theregenerated urea in the form of a slurry is withdrawn from thedecomposition vessel 17 through line 53 and is fed to solid-liquidseparator 55 which is equipped with solidliquid separating means, wherethe urea is separated and is then washed with 9,000 kg./hr. of toluene56, after which the urea is withdrawn and recycled through line 3 intothe reactor 7. Thus the adduction cycle is repeatedly continued. Theliquid portion from the solidliquid separator 55 contains toluene andn-paratfins and is sent through line 57 to storage vessel 49 from whereit may be fed through line 51 to the decomposition vessel 17, or fed tosolvent recovery tower 59. The top fraction from the solvent recoverytower 59 is fed through line 61 to the distillation tower 33 and bottomfraction from the solvent recovery tower 59 is fed through line 63 todistillation tower 65, where the toluene is distilled 011 and recovered.Normal parafiins are collected from the bottom of distillation tower 65at the rate of 2,240 kg./hr. and are stored in vessel 67. If desired, aportion of n-paratlin stored in vessel 67 may be sent through line 69 tobe mixed with the contact oil charged into the Ietreatment vessel 17through line 35; also a poition of the filtrate withdrawn from thesolid-liquid separator 39 through line 43 may be added to the contactoil through lines 71 and 69.

The contact oil which has been separated as filtrate in the solid-liquidseparator 39 and then stored in vessel 49 is fed through line 73 ascharge stock 2. Deparaffined oil is produced at the rate of 9,370kg./hr.

Thus an economical method for separating n-paraflins from hydrocarbonoil where the n-paraffins are obtained in high purity and in high yieldhas been provided by the present invention. While the invention has beendescribed by reference to particular examples, many modi ficat-ions andvariations in the operating pressures which will be apparent to thoseskilled in the art may be made without departing from the scope andspirit of this invention.

What we claim and desire to secure by Letters Patent is:

1. A process for the separation of n-paraffins from a distillatehydrocarbon oil by means of powdered urea, which comprises (a) treatingsaid hydrocarbon oil with said urea in the presence of an activatorsolvent consisting essentially of 3 to 30 percent by volume of methanoland 70 to 97 percent by volume of aromatic hydrocarbon having from 6 to8 carbon atoms per molecule, said activator solvent being present in anamount of to 40 percent by volume based on the volume of saidhydrocarbon oil,

(b) separating the thus-formed'urea adduct from the liquid mixture,

(c) washing said adduct with said aromatic hydrocarbon,

(d) decomposing said adduct by heating a mixture of said adduct and 1.5to 5.0 volumes per volume of said adduct in a decomposition mediumconsisting essentially of 5 to 30 percent by volume of nparafiins and70-97 percent by volume of said aromatic hydrocarbon at a temperatureabove 60 C. but below the dissociation temperature of said adduct, and

(e) separating thus regenerated urea from the liquid mixture.

2. Process according to claim 1 which is continuous and wherein saidn-parafiins in said decomposition medium are obtained from a previousseparation of said hydrocarbon oil by urea adduction, and whereinregenerated urea from step (e) is recycled and used to treat saidhydrocarbon oil in step (a).

3. A process according to claim 1 and the further step of retreatingsaid adduct separated in step (b) by vigorously agitating said adductwith 1.5 to 5 volume of a contact oil per volume of adduct, said contactoil being selected from at least one member of the group consisting of ahydrocarbon charge oil, n-paraffinic oil, a mixture of hydrocarboncharge oil and aromatic hydrocarbon of 6 to 8 carbon atoms, and amixture of n-parafiinic oil and aromatic hydrocarbon of 6 to 8 carbonatoms.

4. A continuous process for the separation of n-parafiins from adistillate hydrocarbon oil by means of powdered urea, which comprises(a) vigorously agitating said hydrocarbon oil with said urea in thepresence of an activator solvent consisting essentially of 3 to 30percent by volume of methanol and 70 to 97 percent by volume of aromatichydrocarbon having from 6 to 8 carbon atoms per molecule, said activatorsolvent being present in an amount of 5 to 40 percent by volume based onthe volume of said hydrocarbon oil to form an n-paraffin-urea adduct,

(b) separating said urea adduct from the liquid mixture,

(c) retreating said adduct by vigorously agitating said adduct with 1.5to 5 volumes of a contact oil per volume of adduct, said contact oilbeing selected from at least one member of the group consisting ofhydrocarbon charge oil, n-parafiinic oil, a mixture of hydrocarboncharge oil and aromatic hydrocarbon of 6 to 8 carbon atoms, and amixture of n-paraflinic oil and aromatic hydrocarbon of 6 to 8 carbonatoms,

(d) separating retreated adduct from said contact oil,

(e) Washing said adduct with said aromatic hydrocarbon,

(f) decomposing said adduct by heating a mixture of said adduct and 1.5to 5.0 volumes per volume of said adduct in a decomposition mediumconsisting essentially of 5 to 30 percent by volume of n-paraffins and70-97 percent by volume of said aromatic hydrocarbon at a temperatureabove C. but below the dissociation temperature of said adduct,

(g) separating thus regenerated urea from the liquid mixture, and

(h) recycling said regenerated urea.

5. A continuous process according to claim 4 wherein said contact oilfor the retreatment of said urea adduct is n-parafiins oil which hasbeen obtained from charge hydrocarbon oil by urea adduction.

6. A continuous process according to claim 4 wherein said contact oilfor retreatment of said urea adduct is n-paratfin oil comprised of amixture of n-parafiins previously separated from hydrocarbon charge oilby urea adduction and paraffinic hydrocarbon having 5 to 8 carbon atoms.

7. A continuous process according to claim 4 wherein said contact oilfor retreatment of said urea adduct is a mixture of n-paraffinspreviously separated from hydrocarbon charge oil and aromatichydrocarbon having 6 to 8 carbon atoms.

8. A continuous process according to claim 4 wherein said contact oilfor the retreatment of said urea adduct is hydrocarbon charge oil.

9. A continuous process according to claim 4 wherein said contact oilfor retreatment of said urea adduct is a mixture of hydrocarbon chargeoil and n-paraffinic oil.

10. A continuous process according to claim 4 wherein said contact oilfor retreatment of said adduct is a mixture of hydrocarbon charge oiland aromatic hydrocarbon of 6 to 8 carbon atoms.

References Cited UNITED STATES PATENTS 2,672,457 3/1954 Weedman 2606762,861,941 11/1958 Jancosek et a1. 20825 2,862,868 12/1958 Brown et al20825 2,879,220 3/1959 Arnold et a1 20825 2,890,161 6/1959 Brown et al20825 2,911,350 11/1959 Kerns 20825 HERBERT LEVINE, Primary Examiner US.Cl. X.R. 26096.5, 676

